1. Field of the Invention
The present invention relates to a fabrication method of a semiconductor device. More particularly, the method relates to a wafer surface protection.
2. Description of the Related Art
In the back-end stage of the conventional wafer manufacturing process, a wafer back lapping is conducted after passing the wafer acceptance test and before the wafer is delivered to customers. The purpose of back lapping is to facilitate the wafer dicing and packaging. The back lapping procedure is a substantially polluting process, therefore, the wafer is easily contaminated.
FIG. 1 is a cross-sectional view showing the fabrication of a semiconductor device according to the prior art. Referring to FIG. 1, a wafer 100 is provided. A bonding pad 102 is formed on the wafer 100. A first passivation layer 104 is formed on the bonding pad 102 and the wafer 100. A second passivation layer 106 is further formed on the first passivation layer 104. The second passivation layer includes a polyimide layer. The second passivation layer 106 is then patterned to form an opening 108 above the bonding pad 102. Debris, for example polyimide residues 120, usually remain on the surface of bonding pad 102. The polyimide residues 120 are commonly removed by performing a descum ash process.
To prevent the wafer from being contaminated and being damaged during polluting processes such as the subsequent back lapping process, an adhesive tape is adhered onto the front surface of the wafer 100 for protection. However, adhesive residues usually remain on the wafer 100 after the adhesive tape is removed after the back lapping process is completed. The adhesive residues remaining on the wafer surface also cause a defective pad bonding and may generate other problems during packaging processes.
Although eliminating the step of the descum ash process before the back lapping process may reduce the adhesive residues, the descum ash process is however essential in the removal of the polyimide residues 120, which also cause the pad bonding problems.
Accordingly, this invention provides a method for protecting a wafer from debris remaining on the surface after a polluting process is completed. The wafer comprises a front surface and a rear surface, wherein a process that is conducted on the rear surface of the wafer may induce contamination of the front surface of the wafer. A non-adhesive protective film is therefore formed to cover the front surface of the wafer. An adhesive tape is further adhered to the protective film. After the process which may cause contamination of the wafer surface is completed, the adhesive tape along with the protective film is removed. The process that induces contamination of the wafer surface includes chemical mechanical polishing on the rear surface of the wafer.
The non-adhesive protective film, including polyethylene (PE) or polyvinyl chloride (PVC) for example, is formed by spraying a liquid protective film on the front surface of the wafer. The protective liquid film then solidifies to a solid and non-adhesive film after exposure to air. To ensure uniform distribution, the wafer rotates while spraying the liquid protective film. The duration of air exposure is about 3 to 5 minutes.
The wafer surface protection method according to the present invention is simple, in which the non-adhesive protective film can be removed along with the adhesive tape. The problem of debris such as conventional adhesive residues remaining on the surface of the wafer, which cause a defective pad bonding, is prevented.
Furthermore, according to the present invention, a descum ash process an be further performed before the application of the protective film to remove polyimide residues, because polyimide residues also cause a defective pad bonding.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.